The present invention relates to structural panel assemblies, and particularly to an improved insulated structural panel incorporating a pair of oppositely located structurally reinforced load-bearing skins.
The ever-increasing cost of obtaining useful heat energy from sources such as oil, coal, wood, and the sun has caused a great deal of effort to be directed to the design of building enclosures having low thermal conductivity, for the retention or exclusion of heat. Some builders have increased wall thicknesses by using wider stud members, increasing wall thickness to measurements as great as 24 inches, in order to accommodate insulating materials such as fiberglass. Such construction is undesirably expensive, in terms of the cost of insulating materials, the amount of heat conducted through building wall stud members, and the labor used to build an enclosure having sufficient structural strength and insulation. In addition, such large cavities filled with loose insulating material in floors, walls, ceilings, and roof spaces create concern over proper ventilation, control of fires, control of insect and rodent infestation, and control and exclusion of humidity and prevention of thermal cycling within the interior portion of the panels and air infiltration into the building through the effects of vacuum and pressures caused by wind and heated air rising and finding an outlet to the outside. Maintenance costs, particularly in the event any of the enclosed material volume becomes wet or is infested with vermin, could be sizable, and repair could be difficult to accomplish. Fires in such large cavities in floors, walls, or roofs, would be quick to spread and difficult to control, and may result in rapid impairment of the structural system of the building. Recently, building codes have required that panel skins and/or the thermal barriers must remain in place for certain periods of time depending on the particular code classification of the building.
Some builders have recently begun using post-and-beam construction combined with insulated structural panels having a pair of parallel skin members of plywood and the like, interconnected and insulated by expandable plastic foam, using the panels to close the spaces defined by the post-and-beam structures. Such panels, however, have a limited amount of aesthetic appeal in architectural designs and as interior finishing panels, and such panels make only a limited contribution to structural strength.
Other building panels in use in home construction, smaller office buildings, and cold storage structures, have frames of lumber to carry structural loads, to which are attached exterior and interior plywood panel faces, with the spaces between the panel faces being filled with various insulating materials. The opposite panel faces are, thus, interconnected by wooden load-bearing members which span the entire distance between the opposite panel faces. Building panels of such construction are able to support considerable loading and are usable as floor, wall and roof panels. Such construction, however, still permits too great an amount of heat to be conducted between panel faces through the structural strength members in such building panels.
These and other related problems have been dealt with more or less satisfactorily in the past, as is shown, for example, in Jamison U.S. Pat. No. 4,471,591, which discloses a wall assembly having studs located alternately on opposite sides of a wall, with cured foam insulation located along an exterior side skin, and conventional fiberglass batts filling the space between the foam and an interior skin. Peterson U.S. Pat. No. 4,224,774 discloses a structural column member built up of a pair of dimension lumber stud elements joined by a core of mineral fibers bonded together by a resin. This structural member is used to support the inner and outer face coverings of a wall or the like, with apparently fibrous insulating material filling the remainder of the interior of the wall.
Turner, Jr. U.S. Pat. No. 4,285,184 discloses a wall construction including alternately located studs supporting the opposite skins of the wall, with the space between the skins being filled with an unspecified thermal insulating material. Coutu, Sr. U.S. Pat. No. 4,443,988 and Day et al. U.S. Pat. No. 4,147,004 disclose composite wall panels including skins of wood sheet material bonded adhesively to rigid expanded foam core material. LeMaitre U.S. Pat. No. 4,395,853 discloses a roof structure including a pair of opposite metal skins spaced apart from each other by metal spacers, with thermal insulation being located between the skins.
Butcher U.S. Pat. No. 3,258,889 discloses a prefabricated building panel in which closed cell foam is used to fasten a skin to one side of a frame structure for a wall of a mobile home.
None of the above-mentioned structures, however, has fully met the need for a building panel which is acceptably strong, light, and thermally insulative, yet low in cost and able to maintain structural integrity when subjected to the stresses of a harsh climate, high winds, structural loadings and earthquake loading.